Vaccines for Chlamydia psittaci infections

ABSTRACT

Vaccine compositions protective against  Chlamydia psittaci  infections in animals, including but not limited to humans and avian species, comprising an immunogenic amount of a  C. psittaci  major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2 are provided. Nucleic acid vectors for the expression of MOMP polypeptides and MOMP polypeptide fusion proteins are disclosed. Nucleic acid vectors encoding a  C. psittaci  major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2 useful for genetic, or “naked nucleic acid” vaccination are disclosed. Methods for preventing a  Chlamydia psittaci  infection in a subject using MOMP polypeptides, MOMP polypeptide-fusion proteins, or nucleic acid expression vectors are also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to Chlamydia psittaci vaccines and to methods of protecting animals, including avian species, from Chlamyida psittaci infections.

2. Background Art

The genus Chlamydia contains four species of obligate parasitic bacteria: Chlamydia psittaci, Chlamydia pecorum, Chlamydia pneumoniae, and Chlamydia trachomatis. This unique genus causes a variety of diseases in humans, mammals, and birds. In humans, the most notable are trachoma and urogenital infections due to C. trachomatis and psittacosis caused by C. psittaci. In animals, C. psittaci can cause a diverse range of disease in livestock, poultry, turkeys and companion birds. The known C. psittaci strains have been grouped into eight biovars (Perez-Martinez, J A and J Storz, 1985). Strains of serovar 1 are mainly associated with intestinal infections and abortions, while strains of serovar 2 cause polyarthritis, encephalitis, and conjunctivitis in ruminants. Avian strains of C. psittaci cause respiratory problems and diarrhea in birds (Storz, 1988). The organism can also be transmitted to humans from these animals, and outbreaks have been documented in animal production workers. Thus, there is a need for an effective vaccine against C. psittaci for mammalian and avian species.

The chlamydia organism goes through two developmental stages in its life cycle. The extracellular form, which is the infectious entity of the cycle, is called the elementary body (EB). These EBs attach and enter the host cell, where they re-organize into reticulate bodies (RBs) which divide within membrane-bound host cell compartments by binary fission and then condense into a new generation of infectious EBs. The attachment and entry of the EB into the host cell is a receptor-mediated phenomenon (Hodinka et al. 1988), and several chlamydial proteins have been implicated in the EB attachment to host cellular membranes (Baghian and Schnorr, 1992). One of these proteins is called the “major outer membrane protein”, or MOMP, and surface-exposed epitopes of this protein from C. trachomatis have been shown to block EB attachment onto the host cell (Su and Caldwell, 1991). The MOMP genes from some strains of C. psittaci and C. trachomatis have been sequenced (Baehr et al., 1988, Pickett et al. 1988, Yuan et al. 1989, Zhang et al. 1989, Kaltenboeck, et al. 1993). Analyses of these sequences revealed that portions of the structure of this protein are conserved between species. There are also four regions of “variable domain” interspersed with conserved sequences, and these are referred to as VD1, VD2, VD3, and VD4. The location of these VD1 regions are identical in the two species (see Zhang et al., 1989). A comparison of the genes encoding the MOMP from C. psittaci and C. trachomatis show that, overall, the sequences are approximately 68% identical.

In C. trachomatis, these four variable regions have been shown to be involved in the neutralization of EB infectivity, in serotype specificity, (Baehr, et al. 1988; Peeling et al. 1984; and Spears and Storz 1979) as well as in the pathogenicity of the strains (Baehr et al. 1988 and Su et al. 1988). Nonetheless, the development of subunit vaccines for C. trachomatis has been hampered by the difficulty in expressing the native, full-length MOMP gene in a recombinant vector host (Manning and Stewart, 1993). There is no known published work on the expression of the C. psittaci MOMP gene prior to that described herein. Consequently, there remains a need to develop an effective subunit vaccine for animal and avian species to protect them from C. psittaci infections.

SUMMARY OF THE INVENTION

The present invention provides a vaccine composition which is protective against Chlamydia psittaci infections in animals, including avian species, comprising an immunogenic amount of a C psittaci major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2. Also provided are polypeptides and isolated nucleic acids encoding such polypeptides, as well as methods of preventing C. psittaci infections in animals comprising administering to the subject animal such vaccine compositions.

Also provided are nucleic acid vectors for the expression of a MOMP polypeptide-MBP fusion protein comprising a nucleic acid encoding MBP and a nucleic acid encoding an immunogenic C. psittaci MOMP polypeptide arranged in tandem such that the MOMP-MBP fusion protein can be expressed.

Additionally provided are methods of preventing a Chlamydia psittaci infection in a subject comprising administering to the-subject a nucleic acid vaccine comprising an immunizing amount of a nucleic acid vector comprising a nucleic acid encoding an immunogenic C. psittaci MOMP polypeptide lacking regions VD1 and VD2.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

“MOMP” means the major outer membrane protein from a Chlamydia psittaci strain.

As used herein, the term “polypeptide” refers to a polymer of amino acids. As used in combination with MOMP, it means a fragment of MOMP.

As used in the specification and in the claims, “a” can mean one or more, depending upon the context in which it is used.

Maltose Binding Protein, or “MBP” means a maltose binding protein.

The term “immunogenic amount” means an amount of an immunogen, i.e., a MOMP polypeptide, a MOMP polypeptide-MBP fusion protein, or portions thereof, which is sufficient to induce an immune response in a vaccinated animal and which protects the animal against active infection with Chlamydia psittaci upon exposure thereto.

The term “immunizing amount” means an amount of a nucleic acid expression vector sufficient to induce an immune response in a vaccinated animal and which protects the animal against active infection with Chlamydia psittaci upon exposure thereto.

DETAILED DESCRIPTION

Vaccine preparations that are efficacious and economical for use in human and non-human animals, including birds, such as chickens, turkeys and companion birds, are provided.

Polypeptide Vaccines

The present invention provides a vaccine composition which is protective against Chlamydia psittaci infections in animals, including avian species, comprising an immunogenic amount of a C. psittaci major outer membrane protein (MOMP) polypeptide lacking variable regions VD1 and VD2. In specific embodiments, the vaccine composition can comprise an immunogenic amount of a C. psittaci major outer membrane protein (MOMP) polypeptide comprising amino acids 183 through 402 of the MOMP protein from C. psittaci strains Avian Type C, LSUWTCK (a strain isolated from a cockatiel which has the identical MOMP gene sequence to Avian Type C), or strain 6BC (which is identical to the sequence of Mn except for a single amino acid change), or amino acids 164 to 389 of the MOMP protein from C. psittaci strain B577.

The complete nucleic acid sequences of the MOMP gene from C. psittaci strains Avian Type C, B577, and 6BC are provided herein as SEQ ID NO: 9, SEQ ID NO: 11 and SEQ ID NO: 13, respectively, and the corresponding amino acid sequences of the MOMP proteins are provided herein as SEQ ID NO: 10, SEQ ID NO: 12, and SEQ ID NO: 14, respectively.

The MOMP polypeptide is purified from other proteins sufficiently to induce a specific immune response. Thus, in specific embodiments, the MOMP polypeptide comprising the vaccine comprises the amino acid sequence set forth in SEQ ID NO:1. In another embodiment, the MOMP polypeptide of the vaccine comprises the amino acid sequence set forth in SEQ ID NO:2.

In a specific embodiment of this invention, the MOMP polypeptide is provided as a component of a fusion protein. Thus the present invention provides a vaccine composition comprising a MOMP polypeptide, as described herein, linked to a non-MOMP polypeptide or protein, and a nucleic acid encoding such a fusion protein. A MOMP fusion protein can be made with any desired protein as part of the chimera.

One example is glutathione-S-transferase (“GST”) which is commonly used as a fusion protein. Another example is Maltose Binding Protein (MBP). Thus, in one embodiment, a vaccine composition comprises a Maltose Binding Protein-MOMP fusion protein, wherein the MOMP portion of the fusion protein is a C. psittaci MOMP polypeptide. Such a fusion protein can have MBP as the amino terminal protein of the fusion protein and the MOMP polypeptide as the carboxyl terminal portion of the fusion protein. Specifically provided is a vaccine composition comprising an MBP-MOMP fusion protein which includes the polyamino acid encoded by nucleotides 1606-2661 of the MBP sequence from the E. coli malE gene (available, for example, in the vector pMAL™-c2 from New England Biolabs, Inc., Beverly, Mass. 01915-5999). Also specifically provided is a vaccine composition comprising MBP-MOMP fusion protein wherein the MOMP polypeptide is a C. psittaci MOMP polypeptide comprising amino acids 183 through 402 of the MOMP protein from either C. psittaci strains Avian Type C, LSUWTCK, or 6BC, or amino acids 164 to 389 of the MOMP protein from C. psittaci strain B577. Fusion proteins utilizing MBP sequences are presented in U.S. Pat. No. 5,643,758. The fusion protein of this invention has several advantageous characteristics. The unexpected discovery that such a MBP-MOMP fusion protein precipitates in inclusion bodies in the bacterial host cells provided an economical method for purifying this immunogen. Specifically, for example, this MBP-MOMP fusion protein can be expressed from a nucleic acid encoding it in relatively large amounts (e.g., 100 milligrams per liter of E. coli) in a manner such that the fusion protein can be very easily purified to a useful extent. Typically, MBP-protein fusions are purified by passing the cell extract over an affinity column bound with an appropriate ligand for MBP. The added cost of such a preparation step generally makes such proteins uneconomical as vaccines in production animals. The MBP-MOMP fusion protein of this invention can be prepared to sufficient purity without the use of such a column, making the economical production of a production or companion animal vaccine possible. This MBP-MOMP fusion protein precipitates as inclusion bodies, and thus traditional purification techniques, such as affinity columns, are not necessary, and the resulting purified fusion protein retains immunogenicity.

Polypeptides having amino acid substitutions from the sequences set forth, that do not significantly reduce the immunogenicity of the polypeptides, are contemplated by this invention. For example, amino acid substitutions can be selected by known parameters to be neutral substitutions (see, e.g., Robinson W E Jr, and Mitchell W M., AIDS 4:S151-S162(1990)). As will be appreciated by those skilled in the art, the invention also includes those polypeptides having slight variations in amino acid sequences or other properties. Such variations may arise naturally as allelic variations (e.g., due to genetic polymorphism) or may be produced by human intervention (e.g., by mutagenesis of cloned DNA sequences), such as induced point, deletion, insertion and substitution mutants. Minor changes in amino acid sequence are generally preferred, such as conservative amino acid replacements, small internal deletions or insertions, and additions or deletions at the ends of the molecules. Substitutions may be designed based on, for example, the model of Dayhoff, et al. (in Atlas of Protein Sequence and Structure 1978, Nat'l Biomed. Res. Found., Washington, D.C.). These modifications can result in changes in the amino acid sequence, provide silent mutations, modify a restriction site, or provide other specific mutations. Additionally, the amino acid sequences of the MOMP polypeptide vaccines of this invention can include sequences in which one or more amino acids have been substituted with another amino acid to provide for some additional property, such as to remove/add amino acids capable of disulfide bonding, to increase its bio-longevity, alter enzymatic activity, or alter interactions with gastric acidity. In any case, the peptide must retain C. psittaci protective immunogenicity.

It is also contemplated in this invention that the variable regions VD3 and VD4 can be administered either in the form of a single MOMP polypeptide, for example SEQ ID NO:1 or SEQ ID NO:2, or as multiple MOMP polypeptides, each one encoding one of the variable regions. Techniques for producing such MOMP polypeptides are routine in art, given the knowledge of the full DNA sequence of the MOMP genes. For example, one can construct multiple nucleic acid vectors by first enzymatically cleaving the DNA of the MOMP gene at restriction enzyme sites located on either side and between variable regions VD3 and VD4 and then cloning the resulting DNA fragments into appropriate vectors for expression. Alternatively, as shown in the Examples herein, artificial primers can be designed to amplify the desired portions of the MOMP gene with convenient restriction enzyme recognition sites in the primers, to allow rapid and efficient cloning of selected portions of the MOMP gene into expression vectors.

Selected MOMP polypeptides can be assayed for immunogenicity and specificity. Briefly, various concentrations of a putative immunogenically specific polypeptide are prepared and administered to an animal and the immunological response (e.g., the production of antibodies or cell mediated immunity) of an animal to each concentration is determined. The amounts of antigen administered depend on the subject, e.g., a human or a non-human animal, including a bird, the condition of the subject, the size of the subject, etc. Thereafter an animal so inoculated with the antigen can be exposed to the bacterium to test the potential vaccine effect of the specific immunogenic MOMP polypeptide. The specificity of a putative immunogenic MOMP polypeptide can be ascertained by testing sera, other fluids or lymphocytes from the inoculated animal for cross-reactivity with other closely related bacteria.

Nucleic Acids

The present invention provides an isolated nucleic acid comprising a nucleic acid which encodes a C. psittaci MOMP polypeptide lacking VD1 and VD2. In a specific embodiment, the nucleic acid includes the variable regions VD3 and VD4 (e.g., amino acids 183 to 402 of the C. psittaci Avian Type C, LSUWTCK, or 6BC MOMP protein, or amino acids 162 to 389 of the C. psittaci B577 MOMP protein. Additionally, the amino terminus end of the isolated nucleic acid can be modified from the native sequence to include an ATG (methionine) start codon and a Kozak regulatory sequence, both of which are typically required for translation in eukaryotes.

In a specific embodiment, the present invention provides an isolated nucleic acid comprising a nucleic acid having the nucleotide sequence set forth in SEQ ID NO:3. This nucleic acid encodes roughly the carboxyl-terminal half of the C. psittaci strain Avian Type C MOMP protein and includes VD3 and VD4. Additionally, the amino terminus end of this sequence has been modified from the native sequence to include an ATG (methionine) start codon and a Kozak regulatory sequence. Another embodiment of this invention provides an isolated nucleic acid having the nucleotide sequence set forth in SEQ ID NO: 4, which ends at the stop codon TAA, and thus does not include the 3′ untranslated sequences included in SEQ ID NO:3.

In another embodiment, the present invention provides an isolated nucleic acid comprising a nucleic acid having the nucleotide sequence set forth in SEQ ID NO: 5. This nucleic acid encodes roughly the carboxyl-terminal half of the C. psittaci strain B577 MOMP protein and includes VD3 and VD4, and additionally has an ATG (methionine) and a Kozak consensus sequence at the amino terminus of this polypeptide. Another embodiment of this invention provides an isolated nucleic acid having the nucleotide sequence set forth in SEQ ID NO: 6, which ends at the stop codon TAA, and thus does not include the 3′ untranslated sequences included in SEQ ID NO:5.

The present invention also provides a composition which is protective against C. psittaci infections comprising polypeptides expressed in a suitable host by one or more of the isolated nucleic acids of this invention and a pharmaceutically acceptable carrier.

Also provided is a nucleic acid vector for the expression of a MOMP polypeptide-MBP fusion protein comprising a nucleic acid encoding MBP and a nucleic acid encoding a MOMP polypeptide arranged in tandem such that the MOMP-MBP fusion protein can be expressed. In a specific embodiment, the nucleic acid encodes an amino acid sequence for the MOMP polypeptide selected from the group consisting of: SEQ ID NO:1 and SEQ ID NO:2. In a preferred embodiment, the nucleic acid encoding MBP is located 5′ to the nucleic acid encoding MOMP. Persons skilled in the art are knowledgeable in arranging the nucleic acids such that the fusion protein can be expressed, including ensuring that the reading frame for both nucleic acids is the same, and including various control regions, as also further discussed herein.

In another embodiment, the present invention provides a nucleic acid vector for the transient expression of a C. psittaci MOMP polypeptide in a eukaryotic cell comprising a eukaryotic promoter functionally linked to a nucleic acid encoding a C. psittaci MOMP polypeptide lacking regions VD1 and VD2. In a specific embodiment, the nucleic acid encodes an amino acid sequence selected from the group consisting of: SEQ ID NO:7 or SEQ ID NO:8. In a further specific embodiment, the nucleic acid has a sequence selected from the group consisting of: SEQ ID NO:3; SEQ ID NO:4, SEQ ID NO:5 and SEQ ID NO:6. Any desired eukaryotic promoter can be utilized; however, preferable promoters are those that are strong promoters in avian or mammalian cells, as are known in the art and further described below. As discussed herein, certain modifications to the nucleic acid vectors can be made.

In a specific embodiment, provided herein is a nucleic acid vector for the transient expression of a C. psittaci MOMP polypeptide in a eukaryotic cell comprising a cytomegalovirus promoter functionally linked to a nucleic acid encoding a C. psittaci MOMP polypeptide lacking regions VD1 and VD2. In a further specific embodiment, the nucleic acid encodes an amino acid sequence selected from the group consisting of: SEQ ID NO:7 and SEQ ID NO:8.

Nucleic Acid Vaccines

The present invention provides compositions comprising a plurality of the nucleic acid vectors for the transient expression of a C. psittaci MOMP polypeptide in a eukaryotic cell comprising a eukaryotic promoter functionally linked to a nucleic acid encoding amino acid sequence comprising a C. psittaci major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2. Such compositions are administered to a subject such that they can be expressed in the subject, the “plurality” of vectors being sufficient to induce an immune response.

In a specific embodiment, the present invention provides a composition which is protective against a Chlamydia psittaci infection in animals, including avian species, comprising a plurality of nucleic acid expression vectors comprising a eukaryotic promoter functionally linked to a nucleic acid encoding the amino acid sequence set forth in SEQ ID NO:7 or SEQ ID NO:8 in a pharmaceutically acceptable carrier.

In a further specific embodiment, the present invention provides a composition which is protective against Chlamydia psittaci infections in animals, including avian species, comprising a plurality of nucleic acid expression vectors comprising a eukaryotic promoter functionally linked to one or more nucleotide sequences selected from the group consisting of: SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5 and SEQ ID NO:6 in a pharmaceutically acceptable carrier.

In a specific embodiment, the nucleic acid expression vector comprises a cytomegalovirus promoter functionally linked to a nucleic acid encoding VD3 and VD4 of MOMP, for example having the nucleotide sequence set forth in either SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5 or SEQ ID NO:6.

Nucleic Acids/Vectors/Vaccines-General

The nucleic acid encoding the MOMP polypeptide can be any nucleic acid that functionally encodes the MOMP polypeptide. For example, to functionally encode, i.e., allow the nucleic acid to be expressed, the nucleic acid can include, for example, expression control sequences, such as an origin of replication, a promoter, an enhancer, and necessary information processing sites, such as ribosome binding sites, RNA splice sites, polyadenylation sites, and transcriptional terminator sequences. Preferred expression control sequences are strong and/or inducible promoters such as those derived from metallothionine genes, actin genes, immunoglobulin genes, CMV, SV40, Rous sarcoma virus, adenovirus, bovine papilloma virus, etc. A nucleic acid encoding a selected MOMP polypeptide can readily be determined based upon the genetic code for the amino acid sequence of the selected MOMP polypeptide, and, clearly, many nucleic acids will encode any selected chimeric protein. Modifications to the nucleic acids of the invention are also contemplated, since mutations can thereby be studied for greater protective vaccine effect. Additionally, modifications that can be useful are modifications to the sequences controlling expression of the MOMP polypeptide to make production of the MOMP polypeptide inducible or repressible upon addition to the cells of the appropriate inducer or repressor. Such means are standard in the art (see, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1989). The nucleic acids can be generated by means standard in the art, such as by recombinant nucleic acid techniques, as exemplified in the examples herein, and by synthetic nucleic acid synthesis or in vitro enzymatic synthesis.

The expression vectors of the invention can be in a host capable of expressing the MOMP polypeptide immunogen or the MBP-MOMP fusion protein immunogen. There are numerous E. coli expression vectors known to one of ordinary skill in the art useful for the expression of the antigen. Other microbial hosts suitable for use include bacilli, such as Bacillus subtilus, and other enterobacteriaceae, such as Salmonella, Serratia, and various Pseudomonas species. In these prokaryotic hosts one can also make expression vectors, which will typically contain expression control sequences compatible with the host cell (e.g., an origin of replication). In addition, any number of a variety of well-known promoters will be present, such as the lactose promoter system, a tryptophan (Trp) promoter system, a beta-lactamase promoter system, or a promoter system from phage lambda. The promoters will typically control expression, optionally with an operator sequence, and have ribosome binding site sequences for example, for initiating and completing transcription and translation. If necessary an amino terminal methionine can be provided by insertion of a Met codon 5′ and in-frame with the antigen. Also, the carboxyl-terminal extension of the antigen can be removed using standard oligonucleotide mutagenesis procedures.

Additionally, yeast expression systems can be used. There may be several advantages to yeast expression systems. First, evidence exists that proteins produced in a yeast secretion systems exhibit correct disulfide pairing. Second, post-translational glycosylation is efficiently carried out by yeast secretory systems. The Saccharomyces cerevisiae pre-pro-alpha-factor leader region (encoded by the MF α-1 gene) is routinely used to direct protein secretion from yeast (Brake et al., 1984). The leader region of pre-pro-alpha-factor contains a signal peptide and a pro-segment which includes a recognition sequence for a yeast protease encoded by the KEX2 gene: this enzyme cleaves the precursor protein on the carboxyl side of a Lys-Arg dipeptide cleavage-signal sequence. The antigen coding sequence can be fused in-frame to the pre-pro-alpha-factor leader region. This construct is then put under the control of a strong transcription promoter, such as the alcohol dehydrogenase I promoter or a glycolytic promoter. The antigen coding sequence is followed by a translation termination codon which is followed by transcription termination signals. Alternatively, the antigen coding sequences can be fused to a second protein coding sequence, such as Sj26 or β-galactosidase, used to facilitate purification of the fusion protein by affinity chromatography. The insertion of protease cleavage sites to separate the components of the fusion protein is applicable to constructs used for expression in yeast.

Additionally, mammalian cells permit the expression of proteins in an environment that favors important post-translational modifications such as folding and cysteine pairing, addition of complex carbohydrate structures, and secretion of active protein. Vectors useful for the expression of antigen in mammalian cells are characterized by insertion of the antigen coding sequence between a strong viral promoter and a polyadenylation signal. The vectors can contain genes conferring either gentamicin or methotrexate resistance for use as selectable markers. The antigen and immunoreactive fragment coding sequence can be introduced into a Chinese hamster ovary cell line using a methotrexate resistance-encoding vector. Presence of the vector DNA in transformed cells can be confirmed by Southern analysis and production of an RNA corresponding to the antigen coding sequence can be conformed by Northern analysis. A number of other suitable host cell lines capable of secreting intact human proteins have been developed in the art, and include the CHO cell lines, HeLa cells, myeloma cell lines, Jurkat cells, etc. Expression vectors for these cells can include expression control sequences, such as an origin of replication, a promoter, an enhancer, and necessary information processing sites, such as ribosome binding sites, RNA splice sites, polyadenylation sites, and transcriptional terminator sequences. Preferred expression control sequences are promoters derived from immunoglobulin genes, SV40, Adenovirus, Bovine Papilloma Virus, etc. The vectors containing the DNA segments of interest can be transferred into the host cell by well-known methods, which vary depending on the type of cellular host. For example, calcium chloride transfection is commonly utilized for prokaryotic cells, whereas calcium phosphate treatment or electroporation may be used for other cellular hosts.

Alternative vectors for the expression of antigen in mammalian cells, those similar to those developed for the expression of human gamma-interferon, tissue plasminogen activator, clotting Factor VII, hepatitis B virus surface antigen, protease Nexinl, and eosinophil major basic protein, can be employed. Further, the vector can include cytomegalovirus (CMV) promoter sequences and a polyadenylation signal available for expression of inserted DNAs in mammalian cells.

The nucleic acid vectors for transient expression in a eukaryotic cell are suitable for genetic, or “naked nucleic acid”, immunization. These can be constructed using any of a variety of eukaryotic promoters, herein also referred to as cis-acting transcription/translation regulatory sequences, known in the art. General methods for the construction, production and administration of nucleic acid vaccines are known in the art, e.g. Vogel, FR and N Sarver (1995) Clin. Microbiol. Rev. 8:406-410.

These nucleic acid vectors comprise nucleic acids that functionally encode, i.e. are functionally linked to a nucleic acid encoding a MOMP polypeptide. For example, to functionally encode, i.e., allow the nucleic acid to be expressed, the nucleic acid can include, for example, expression control sequences, such as a cis-acting transcription/translation regulatory sequence (comprising one or more of the following: a promoter, response element(s), an initiator sequence), an enhancer, and information processing sites, such as ribosome binding sites, RNA splice sites, intron elements, polyadenylation sites, and transcriptional terminator sequences, all of which, either alone or in combinations, are capable of directing expression in the target animal. Preferred expression control sequences are strong and/or inducible cis-acting transcription/translation regulatory sequences such as those derived from metallothionine genes, actin genes, myosin genes, immunoglobulin genes, cytomegalovirus (CMV), SV40, Rous sarcoma virus, adenovirus, bovine papilloma virus, etc. The C psittaci MOMP-encoding nucleic acid and expression control sequences are constructed in a vector, such as a plasmid of bacterial origin, for administration to the target animal. There are numerous plasmids known to those of ordinary skill in the art useful for the production of nucleic acid vaccine plasmids. A specific embodiment employs constructs using the plasmid “pcDNA3.1+” as the vector (InVitrogen Corporation, Carlsbad, Calif.). In addition, the nucleic acid expression vectors that functionally encode a MOMP polypeptide may additionally contain immunostimulatory sequences (“ISS”) that stimulate the animals' immune system. Other possible additions to the nucleic acid expression vectors include nucleic acid sequences encoding cytokines, such as granulocyte macrophage colony stimulating factor (GM-CSF) or interleukin-12 (IL-12). The cytokines can be used in various combinations to fine-tune the response of the animal's immune system, including both antibody and cytotoxic T lymphocyte responses, to bring out the specific level of response needed to protect the animal from the targeted disease.

Alternatively, the nucleic acid expression vectors can be constructed in a non-replicating retroviral vector, such as the Moloney murine leukemia virus (N2) backbone described by Irwin, et al. (1994, J. Virology 68:5036-5044).

The present genes were isolated from C. psittaci; however, homologs from any Chlamydia strain infecting a selected species, can readily be obtained by screening a library from that Chlamydia strain, genomic or cDNA, with a probe comprising sequences of the nucleic acids set forth in the sequence listing herein, or fragments thereof, and isolating genes specifically hybridizing with the probe under preferably relatively high stringency hybridization conditions. For example, high salt conditions and/or high temperatures of hybridization can be used. For example, the stringency of hybridization is typically about 5° C. to 20° C. below the T_(m) (the melting temperature at which half of the molecules dissociate from its partner) for the given chain length. As is known in the art, the nucleotide composition of the hybridizing region factors in determining the melting temperature of the hybrid. For 20mer probes, for example, the recommended hybridization temperature is typically about 55-58° C. Additionally, the C. psittaci MOMP sequence can be utilized to devise a probe for a homolog in any specific animal by determining the amino acid sequence for a portion of the C. psittaci protein, and selecting a probe with optimized codon usage to encode the amino acid sequence of the homolog in that particular animal.

The present invention contemplates cells containing a nucleic acid expression vector of the invention. A cell containing a nucleic acid expression vector encoding a MOMP polypeptide typically can replicate the DNA and, further, typically can express the encoded MOMP polypeptide. The cell can be a prokaryotic cell, particularly for the purpose of producing quantities of the nucleic acid, or a eukaryotic cell, particularly a mammalian cell. The cell is preferably a mammalian cell for the purpose of expressing the encoded protein so that the resultant produced protein has mammalian protein processing modifications. The cell also can be a eukaryotic cell in a host organism, for the purposes of vaccinating the host via genetic or “naked nucleic acid” immunization. In the case of genetic immunization, the nucleic acid expression vector does not typically replicate in the host.

In one embodiment, a nucleic acid expression vector of this invention is administered in combination with one or more other nucleic acid vectors, as a “naked nucleic acid immunization” to protect against multiple viral diseases. In a specific embodiment for vaccinating birds, the other viral diseases can be avian polyomavirus, Pacheco's disease virus, or psittacine beak and feather disease virus.

In another specific embodiment, the vaccine composition comprising an immunogenic amount of a C. psittaci major outer membrane protein (MOMP) polypeptide lacking variable regions VD1 and VD2 is administered in combination with one or more recombinant viral proteins from viruses that infect and cause disease in psittacine birds.

Any vaccine composition of this invention can further comprise an adjuvant suitable for use in the species to which the vaccine is to be administered, such as avian or mammalian species. Examples of such adjuvants include but are not limited to a cytokine, such as a lymphokine, a monokine or a chemokine, or a cytokine inducer or an agent that facilitates the entry of the antigen into the cytoplasm of the cell. Other examples of adjuvants that can useful in the present invention include but are not limited to plasmid DNA or bacterial agents. An adjuvant can also include, for example, immunomodulators and co-stimulatory molecules. Additional adjuvants include any compound described in Chapter 7 (pp 141-227) of ‘Vaccine Design, The Subunit and Adjuvant Approach’ (eds. Powell, M. F. and Newman, M. J.) Pharmaceutical Biotechnology, Volume 6, Plenum Press (New York).

Any vaccine composition of this invention can further comprise a pharmaceutically acceptable carrier. By “pharmaceutically acceptable” is meant a material that is not biologically or otherwise undesirable, i.e., the material may be administered to an individual along with the selected compound without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the pharmaceutical composition in which it is contained. A pharmaceutically acceptable carrier can comprise saline or other suitable carriers (Amon, R., (Ed.) Synthetic Vaccines 1:83-92; CRC Press, Inc., Boca Raton, Fla. 1987).

Methods of Vaccination

The present invention further provides methods of vaccinating a subject to induce an immunological response capable of preventing a subsequent C. psittaci infection. The vaccine can be administered to an animal of the avian species, such as poultry, turkeys and companion birds; additionally, particularly for handlers of such avian species, the vaccines can be administered to mammals such as humans. In particular, birds which can be treated by the invention can be any of the various species of birds which are classified as being members of the Psittaciformes order. Examples of such birds include, but are not limited to, Budgerigars (Melopsittacus undulatus), caiques (e.g., Pionites leucogaster leucogaster), macaws (e.g., Ara ararauna), Amazon parrots (e.g., Amazona ochrocephala auropalliata, conures (e.g., Pyrrhara picta, Aratinga wagleri wagleri, Aratinga solstitialis, Aratinga guarouba, Aratinga holochlora rubritorquis or Aratinga acuticaudata acuticaudata), cockatoos (e.g., Cacatua moluccensis, Cacatua ducorps, Cacatua sulphura, Cacatua goffini or Cacatua alba), Splendid Parakeets (Neophema splendida), Pionus Parrots (Pionus maximillani), African Grey Parrots (Psittacus erithacus erithacus, Eclectus Parrots (Electus roratus), Cockatiels (Nymphicus hollandicus) and parakeets (e.g. Psittacula krameri krameri).

Thus, the present invention provides a method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject a vaccine comprising an immunogenic amount of a C. psittaci major outer membrane protein (MOMP) polypeptide lacking variable regions VD1 and VD2. In a specific embodiment, the method comprises an immunogenic amount of a MOMP polypeptide having an amino acid sequence as set forth in either SEQ ID NO:1 or SEQ ID NO:2. In another embodiment, the method comprises an immunogenic amount of an MBP-MOMP polypeptide fusion protein.

The present invention further provides a method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject a vaccine comprising an immunizing amount of a nucleic acid vector for the transient expression in a eukaryotic cell comprising a eukaryotic promoter functionally linked to a nucleic acid encoding a C. psittaci MOMP polypeptide lacking regions VD1 and VD2 of MOMP. In a specific embodiment, the method comprises a nucleic acid encoding an amino acid sequence as set forth in SEQ ID NO:7 or SEQ ID NO:8.

In a specific embodiment, the present invention provides a method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject a vaccine comprising an immunizing amount of a nucleic acid vector for transient expression in a eukaryotic cell comprising a cytomegalovirus promoter functionally linked to a nucleic acid having the nucleotide sequence set forth in either SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5 or SEQ ID NO:6.

Vaccine compositions can be administered to a subject or an animal model by any of many standard means for administering the particular composition. For example, compositions can be administered orally, sublingually, parenterally (e.g., intravenously), by intramuscular injection, by intraperitoneal injection, topically, transdermally, or the like. Compositions can be administered, for example as a complex with cationic liposomes, encapsulated in anionic liposomes, or encapsulated in microcapsules. Compositions can include various amounts of the selected composition in combination with a pharmaceutically acceptable carrier and, in addition, if desired, may include other medicinal agents, pharmaceutical agents, carriers, adjuvants, diluents, etc. Parental administration, if used, is generally characterized by injection. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions. Actual methods of preparing dosage forms are known, or will be apparent, to those skilled in this art; for example, see Martin, E. W., Ed., Remington's Pharmaceutical Sciences, latest edition, Mack Publishing Co., Easton, Pa.

In one embodiment, a vaccine of this invention, whether a protein or a nucleic acid vaccine, is administered on a regular booster schedule, for example, every six months, to companion birds of the order Psittaciformes. The vaccine may be advantageously administered to such birds orally, such as in pill form, or intranasally in a spray, or intraocularly in a drop. Alternatively, the vaccine-may be administered intramuscularly or subcutaneously.

The following examples are intended to illustrate, but not limit, the invention. While they are typical of those that might be used, other procedures known to those skilled in the art may be alternatively employed.

EXAMPLES Example 1 C. psittaci MOMP Genes

Using PCR primers 5GPF (ACGCATGCAAGACACTCCTCAAAGCC; SEQ ID NO: 15) and 3GPB (ACGAATTCCTAGGTTCTGATAGCGGGAC; SEQ ID NO: 16), a full-length C. psittaci MOMP gene was amplified, cloned and sequenced from a wild-type C. psittaci strain isolated from a cockatiel. The sequence of this cockatiel MOMP gene is identical to the MOMP gene sequences from C. psittaci strain MN and Avian Type C strain (Zhang et al. 1989). Previous work by Kaltenboeck et al. (1993) established that the MOMP gene sequence of C. psittaci strain B577 isolated from an aborted ovine fetus was identical to the MOMP gene sequence from a C. psittaci strain isolated from a parakeet.

Example 2 Vector Constructions

A. MOMP 3′ Gene Fragment Cloning

Primer 3 GPB (ACGAATTCCTAGGTTCTGATAGCGGGAC; SEQ ID NO:15) and primer cBamA (CGGATCCATTACCCAAGGTGTTATGGA; SEQ ID NO:17) were used for PCR amplification of DNA from the cockatiel C psittaci strain (“LSUWTCK”). Primer cBamA was specifically designed to create a BamHI restriction site (GGATCC) for subsequent cloning purposes. For PCR amplification of MOMP DNA from strain B577, primer ParaBamG (TAAAGGATCCGCCATGGCAGC; SEQ ID NO:18), which includes a BamHI site naturally present in the B577 sequence, was used in combination with primer 3GPB. The underlined bases in primer ParaBamG represent changes from the natural B577 sequence that create a start ATG codon and a Kozak consensus sequence.

The PCR-derived DNA fragments, which contain either the C. psittaci strain LSUWTCK MOMP gene fragment extending from nucleotide 540 to nucleotide 1266 (SEQ ID NO:3) or the C. psittaci strain B577 MOMP gene fragment extending from nucleotide 563 to 1249 (SEQ ID NO:5), were separately cloned into a plasmid vector pCR 2.1 (InVitrogen, Inc., Carlsbad, Calif. 92008), which contains a unique BamHI site. The orientation of the each cloned DNA fragment was such that after BamHI digestion an approximately 0.75 kb DNA fragment was produced and used as a source of MOMP DNA for the subsequent manipulations. The fragment from strain LSUWTCK encodes 222 amino acids from the MOMP gene and starts immediately after the second variable epitope (VD2) and includes all downstream regions (see Zhang et al. 1989). The fragment from strain B577 encodes 228 amino acids from the MOMP gene and also includes regions VD3 and VD4.

B. Fusion Protein Vector

A BamHI cockatiel MOMP gene fragment (SEQ ID NO: 3) in pCR 2.1, as described above, was cloned into the BamHI site in the bacterial expression vector pMAL™-c2 (New England Biolabs, Inc., Beverly, Mass. 01915-5999). This is a commercially available vector that is designed to create translation fusions between a cloned gene and the E. coli malE gene, which codes for maltose binding protein (MBP). The BamHI site in the bacterial expression vector pMAL™-c2 is in frame with the MBP gene. The BamHI site in the cBamA synthetic oligonucleotide primer was designed to be in the same reading frame with the MOMP gene. Consequently, the construct described herein will result in the expression of a MBP-MOMP fusion protein.

C. Mammalian Expression Vector

In addition to the engineered restriction enzyme site, primer cBamA has a base change from the native sequence, (G-A), creating a start codon (ATG) in frame with the MOMP coding sequence, so that the ribonucleic acid transcribed from the cloned sequence can be translated in eukaryotic cells. The particular location for the ATG was chosen due to the ability to create a Kozak box consensus sequence, G(A)⁻³ NNATGG(A)₊₄ around the start site, which enhances translatability in eukaryotes. Thus, the same BamHI cockatiel MOMP DNA fragment from plasmid pCR2.1 was also used for cloning into the plasmid pcDNA 3.1 Zeo⁺ (InVitrogen, Carlsbad, Calif.), which is designed for high level stable and transient expression in mammalian hosts. This DNA, designated “pcDNA 3.1 Zeo⁺/CpMOMP”, was used for genetic immunization experiments after purification in CsCl gradients.

Example 3 Expression and Purification of MBP-MOMP Fusion Protein

A. Expression.

Protein production was carried out according to the instructions included in the manual from New England Biolabs, Inc. (Beverly, Mass. 01915-5599), except that cells were harvested after 3 hours of induction with Isopropyl-thio-galactoside (IPTG) with a final concentration of 0.3 mM. The pellet of the cells derived from 500 mL of media was resuspended in 25 mL of lysis buffer: 100 mM NaCl, 1.00 mM Tris HCl pH 8.0, 100 mM EDTA pH 8.0, and 10 mM EGTA pH 8.0. Fresh lysozyme 10 mg/mL (0.5 mL for 500 mL of media) was added and the sample was left on ice for 30 min at which time 1 mL of 25% Triton X100 (T100) was added and left on ice for 5 min. At this time the solution became viscous due to the released DNA.

B. Purification

The unexpected formation of inclusion bodies by the MBP-MOMP fusion protein in E. coli after IPTG induction, made it extremely easy to purify. The resultant solution after cell lysis was sonicated (5 times, 30 sec. each time or until the viscosity was eliminated) and subsequently 50 in L of lysis buffer was added. The sample was centrifuged at 5000 g, 20 min. at +4° C. The supernatant of the sample was discarded and the insoluble part containing the MBP-MOMP fusion protein in the form of inclusion bodies was recovered in the pelleted material. The pellet was washed 2 times with lysis buffer +0.5% T100 (49 mL of lysis buffer plus 1 mL of 25% T100) using a 10 min incubation time at room temperature.

The recovered material was resuspended in 25 mL of Lysis buffer without T100 and stored overnight on ice. The material was centrifuged at 5000 g, 20 min, +4° C., resuspended in 5 mL of Lysis buffer, added 45 mL of 6M urea, subsequently incubated for 15 min at room temperature, and finally centrifuged at 5000 g, 20 min at +4° C. The supernatant was recovered and diluted 1:4 with 5M urea and filtered through an AMICON DIAFLO® Ultrafilter, series XM (Amicon, Lexington, Mass. 02173), which had a molecular weight cutoff at 50,000, until the volume was approximately 10 mL. The total volume was adjusted with 5 M urea to 50 mL and the sample was dialyzed against Phosphate buffer saline (PBS) to decrease the urea concentration in the sample.

The first dialysis step was 2 hours against 100 mL of 2.5 M of urea, and the next 5 steps were against two-fold serially decreasing concentrations of 2.5 M urea. Four additional changes of dialysis buffer were performed using 5000 mL of PBS without urea.

The final product was used for injections. The approximate yield of protein extracted from the cells grown in 1 Liter of media was 100 mg, resulting in a MOMP-MBP fusion protein purity of approximately 85%.

A pool of monoclonal antibodies raised against the C. psittaci strain 6BC and the C. pecorum MOMPs, which reacted with purified, native MOMP proteins from strains B577 and 6BC, also reacted with the MBP-MOMP fusion protein in western assays, demonstrating that the fusion protein retains epitopes found on the native protein. The reaction of the same antibodies with strain B577 and the MBP-MOMP fusion protein containing the MOMP polypeptide from strain LSUWTCK, shows that at least some antibodies can recognize MOMP proteins from different strains.

Example 4

Vaccination

A. Immunoblotting Assay

Cockatiel C. psittaci strain LSUWTCK, grown in Vero cells, was partially purified (Baghian, et al., 1990), resolved in SDS-PAGE and transferred onto nitrocellulose membranes (NCM). Strips cut from the blot were used to evaluate the antibody response to MOMP in vaccinated birds. A rabbit anti-cockatiel IgG produced in the inventors' laboratory was used to detect the cockatiel IgG responses to vaccines. Strips were blocked, reacted with cockatiel serum, then with the rabbit anti-cockatiel IgG followed by exposure to a hydrogen peroxidase conjugated goat anti-rabbit IgG and color-forming substrate.

B. Experimental Vaccination Design

1. Experiment B-1.

A total of 25 cockatiels were used. Five treatment regimes were designated, with five birds per treatment. Group I was the control group, which was not vaccinated. Groups II, III, and IV were vaccinated with the vaccines of this invention. In Group V, the birds were inoculated with inactivated elementary bodies from C. psittaci. The Groups were set up as follows: Group I: No vaccine, control group Group II: pcDNA 3.1 Zeo⁺/CpMOMP DNA vaccine Group III: MBP-MOMP fusion protein vaccine (Example 3A) Group IV: pcDNA 3.1 Zeo⁺/CpMOMP DNA and MBP-MOMP fusion protein combination vaccine Group V: Vaccination with inactivated EBs 2. Experiment B-2

A total of 21 cockatiels were used. Five treatment regimes were designated, with three birds in Group I, five birds each in Groups II and III, and four birds each in Groups IV and V. Group I was the control group, which was not vaccinated. Groups II and III were vaccinated with the vaccines of this invention. In Groups IV and V, the birds were inoculated with inactivated elementary bodies from C. psittaci,

The Groups were set up as follows: Group I: No vaccine, control group Group II: pcDNA 3.1 Zeo⁺/CpMOMP DNA vaccine Group III: MBP-MOMP fusion protein vaccine (Example 3A) Group IV: Vaccination with inactivated (by irradiation) EBs Group V: Vaccination with glutaraldehyde-treated, inactivated EBs C. Vaccination Protocol 1. Experiment B-1

Group I did not receive any vaccinations. For Group II 100 microliters of pcDNA 3.1 Zeo⁺/CpMOMP DNA (1 microgram/microliter) mixed with 100 microliters of PBS. This mixture was injected in 4 sites using 50 microliters/site. For Group m vaccination, 1.7 milliliters (mL) of the MOMP-MBP fusion protein (1 microgram/microliter) was mixed with 1.7 mL Adju-Phos [Aluminum Phosphate Gel adjuvant (Superfos Biosector a/5, Inc., Denmark)], and 0.4 microliters were injected subcutaneously in each bird. For Group IV, each bird simultaneously received the same inoculations of Group II and Group III, therefore a combination “fusion-protein/DNA” vaccine. For Group V, the birds were injected with inactivated elementary bodies from C. psittaci, made according to the protocol described at C.3 below.

2. Experiment B-2.

Group I did not receive any vaccinations. For Group II 100 microliters of pcDNA 3.1 Zeo⁺/CpMOMP DNA (1 microgram/microliter) mixed with 100 microliters of PBS. This mixture was injected as follows: 100 microliters were dropped into the nasal canals, 50 microliters into each side of the nose, and 100 microliters was injected at 3 sites in the chest muscle. For Group III vaccination, 1.7 milliliters (mL) of the MOMP-MBP fusion protein (1 microgram/microliter) was mixed with 1.7 mL Adju-Phos [Aluminum Phosphate Gel adjuvant (Superfos Biosector a/5, Inc., Denmark)], and 0.4 microliters were injected subcutaneously—injections were performed as described for Group II. For Groups IV and V, the birds were injected with inactivated elementary bodies from C. psittaci, inactivated either with cobalt source irradiation, or made according to the protocol in C.3. below, and then further treated by irradiation with a cobalt source.

3. Production of Inactivated EBs: Four mL of a PBS solution containing C. psittaci strain LSUWTCK (1.4×10⁸/mL) were inactivated by treatment in 1 mL of PBS+0.5 mL glutaraldehyde (20%), at 4° C. overnight. EBs were pelleted and washed with 4 mL of PBS, resuspended in 4 mL of PBS, and tested for infectivity in cell culture. Residual infectivity was detected, so the EBs (3 ml) were treated again with 1 ml formaldehyde (final conc. 4%) for 6 hours at room temperature. EBs were again pelleted, washed once with PBS and resuspended in a PBS Adju-Phos (Sigma, Inc.). Each bird was inoculated with 0.5 ml of the final solution subcutaneously.

D. Vaccination Schedule

1. Experiment B-1.

On Oct. 1, 1996, the birds were bled for prevaccination serology tests. On the same day, first injections were given as follows: Group II: intramuscularly Group III: subcutaneously Group IV: as in Group II and III Group V: subcutaneously

On Nov. 4, 1996, the four groups were given second injections, identical to the ones indicated above. On Dec. 19, 1996, the four groups were given third injections, identical to the 1st and 2nd injections. On Jan. 14, 1997, the birds were bled again, then challenged with a 0.5 mL suspension of C. psittaci EBs containing at least 10⁴, preferably 5×10⁵, infection forming units (IFU). These challenges were administered intranasally and by ocular drops, one in each eye.

2. Experiment B-2.

The schedule for this experiment generally paralleled the experiment above.

E. Results

1. Experiment B-1: Seroconversion

Bird sera taken after the third vaccine inoculation, just before the challenge with infectious EBs, were used in a immunoblotting assay. Among the four groups which were vaccinated, only Group III showed consistent seroconversion, in that two birds were strongly positive while three birds were weakly positive. One of the birds in Group V which was vaccinated with inactivated EBs also gave a strong reaction in the immunoblotting assay.

2. Experiment B-1: Protection from Challenge

The birds were evaluated for clinical signs over the months of January through March, 1997 following their challenge inoculation on January 14. The following observations were made:

-   Group I: This group of birds exhibited signs of bilateral     conjunctivitis, irritated choana and stained vents (a sign of     diarrhea). One bird in the group died 38 days post-exposure, and C.     psittaci was cultured from this animal. Most birds in this group     showed clinical improvement after 25 days post-exposure, until they     were sacrificed. -   Group II: The majority of this group showed mild, clinical signs     associated with conjunctivitis, and an irritated choana (upper     respiratory irritation). Little or no gastrointestinal abnormalities     were noted. All birds survived and were sacrificed. -   Group III: Three birds in this group showed very few clinical     abnormalities during the trial, indicating that they were protected     from the challenge. On days 3-5 after the challenge, bilateral     conjunctivitis, irritated choanas and vent staining was apparent.     Two of the birds died during the trial period. -   Group IV: Four birds from this group exhibited minimal     conjunctivitis through the trial period. One bird did show bilateral     conjunctivitis-with severe diarrhea, and it died early in the trial     period. -   Group V: The entire group of birds had bilateral conjunctivitis and     choanal irritation through 75% of the vaccine trial period. This     group of birds survived with minimal upper respiratory clinical     abnormalities. No gastrointestinal abnormalities were noted. All     birds were sacrificed at the end of the trial period.     3. Experiment B-2. Protection from Challenge

Group I birds showed moderate clinical signs of Chlamydia psittaci infection (see the description under Group I in Experiment B-1 above). Groups II and III were rated as being normal, i.e. all birds were clinically normal, except for a rare abnormality noted, such as conjunctivitis or nasal discharge, which were not considered to be treatment-related. Groups IV and V exhibited clinical signs and symptoms that were the same, or more severe than, the control Group I.

Example 5 Vaccination at Sites of Potential Invasion (Mucosal Immunity)

For a more complete immune response, vaccines may be delivered to the animals at the sites of potential invasion by C. psittaci, e.g. the oral or nasal mucosa. In a preferred embodiment, birds may be vaccinated by an intranasal route. Preparations of vaccine, as described in Example 4, can be administered to the nasal mucosa via a spray delivered intranasally to the bird, or through aerosolization of the vaccine. The latter may be effective when a large number of animals is to be vaccinated simultaneously. One of skill in the art will be familiar with the various techniques available and will be able to design a vaccination protocol appropriate for particular animal(s)' needs (see Tizard, Ian; “Veterinary Immunology: An Introduction”, Fourth Edition, 1992, W.B. Saunders Company, Philadelphia, Pa., 498 pp.). Alternatively, the vaccines of this invention can also be administered through the feed or in the drinking water of the animal.

Although the present process has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims.

REFERENCES

-   Baghian, A and K Schnorr. 1992. Detection and antigenicity of     chlamydial proteins which bind eukaryotic cell membrane proteins. -   Baghian, A, L Shaffer, and J Storz. 1990. Antibody response to     epitopes of chlamydial major outer membrane proteins on infectious     elementary bodies and of the reduced polyacrylamide gel     electrophoresis-separated form. Infect. Immun. 58:1379-1383. -   Hodinka, R L, CH Davis, J Choong, P B Wyrick. 1988. Ultrastructural     study of endocytosis of Chlamydia trachomatis by McCoy cells.     Infect. Immun. 56: 1456-1463. -   Kaltenboeck, B, K G Kousoulas, J Storz. 1993. Structures of and     allelic diversity and relationships among the Major Outer Membrane     Protein (ompA) Genes of the four chlamydial species. J. Bacteriol.     175: 487-502. -   Manning, D S and J S Stewart. 1993. Expression of the major outer     membrane protein of Chlamydia trachomatis in Escherichi coli.     Infect. Immun. 61: 4093-4098. -   Peeling, R, I W McClean, R C Brunham. 1984. In vitro neutralization     of Chlamydia trachomatis with monoclonal antibodies to an epitope on     the major outer membrane protein. Infect. Immunol. 46:484-488. -   Perez-Martinez, J A and J Storz. 1985. Antigenic diversity of     Chlamydia psittaci of mammalian origin determined by     microimmunofluorescences. Infect. Immun. 50: 905-910. -   Pickett, M A, M E Ward, I N Clarke. 1988. Chlamydia psittaci ewe     abortion agent: complete nucleotide sequence of the major outer     membrane protein gene. FEMS Microbiol. Lett. 55: 229-234. -   Spears, P and J Storz. 1979. Biotyping of Chlamydia psittaci based     on inclusion morphology and response to diethylamino-ethyl-dextran     and cycloheximide. Infect. Immun. 24: 224-232. -   Storz, J. 1988. Overview of animal diseases induced by chlamydial     infections, p. 167-192 In A L Barron (ed.), Microbiology of     chlamydia. CRC Press, Inc., Boca Raton, Fla. Su, H and HD     Caldwell. 1991. In vitro neutralization of Chlamydia trachomatis by     monovalent Fab antibody specific to the major outer membrane     protein. Infect. Immun. 59: 2843-2845. -   Yuan, Y, Y X Zhang, N G Watkins, H D Caldwell. 1989. Nucleotide and     deduced amino acid sequences for the four variable domains of the     major outer membrane proteins of the 15 Chlamydia trachomatis     serovars. Infect. Immun. 57:1040-1049. -   Zhang, Y X, S G Morrison, H D Caldwell, W Baehr. 1989. Cloning and     sequence analysis of the major outer membrane protein genes of two     Chlamydia psittaci strains. Infect. Immun. 57: 1621-1625. 

1. A vaccine composition which is protective against Chlamydia psittaci infections in animals comprising an immunogenic amount of a C. psittaci major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2.
 2. The vaccine composition of claim 1, wherein the vaccine comprises VD3 and VD4 of MOMP.
 3. The vaccine composition of claim 1, wherein the polypeptide comprises VD3 and VD4 of MOMP.
 4. The vaccine composition of claim 1, further comprising an adjuvant.
 5. The vaccine composition of claim 4, wherein the adjuvant is suitable for use in avian species.
 6. The vaccine composition of claim 1, wherein the amino acid sequence of the MOMP polypeptide is selected from the group consisting of: SEQ ID NO: 1 and SEQ ID NO:
 2. 7. The vaccine composition of claim 1, wherein the polypeptide further comprises a fusion with a maltose binding protein (MOMP).
 8. The vaccine composition of claim 7, wherein the MBP comprises the amino acid sequence of the male E. coli gene.
 9. A Chlamydia psittaci major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2.
 10. The polypeptide of claim 9, comprising VD3 and VD4 of MOMP.
 11. The polypeptide of claim 10 further comprising a fusion with MBP.
 12. An isolated nucleic acid encoding the polypeptide of claim
 9. 13. An isolated nucleic acid encoding the polypeptide of claim
 10. 14. An isolated nucleic acid encoding the polypeptide of claim
 11. 15. An expression vector functionally linked to the nucleic acid of claim
 12. 16. An expression vector functionally linked to the nucleic acid of claim
 13. 17. An expression vector functionally linked to the nucleic acid of claim
 14. 18. The vector of claim 15 in a cell.
 19. The vector of claim 16 in a cell.
 20. The vector of claim 17 in a cell.
 21. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject the vaccine of claim
 1. 22. The method of claim 21, wherein the subject is a bird.
 23. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject the vaccine of claim
 2. 24. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject the vaccine of claim
 3. 25. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject the vaccine of claim
 4. 26. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject the vaccine of claim
 7. 27. A method of preventing a Chlamydia psittaci infection in a subject comprising administering to the subject an immunizing amount of an expression vector comprising a eukaryotic promoter functionally linked to a nucleic acid encoding a C. psittaci major outer membrane protein (MOMP) polypeptide lacking regions VD1 and VD2.
 28. The method of claim 27, wherein the nucleic acid encodes a polypeptide with an amino acid sequence selected from the group consisting of: SEQ ID NO:7 and SEQ ID NO:8.
 29. The method of claim 27, wherein the eukaryotic promoter is the cytomegalovirus promoter. 